body {
    margin: 0;
    padding: 0;
}
.app {
    max-width: 400px;
    margin: 0 auto;
}
.background-container {
    position: relative;
    width: 100%;
    height: auto;
    margin-top: 30px ;
}
.background-container img {
    width: 100%;
    height: 100%;
}
.background-container button {
    position: absolute;
    left: 50%;
    bottom: 10%;
    width: 250px;
    height: 50px;
    background: #fff;
    border: none;
    font-size: 18px;
    font-weight: 600;
    border-radius: 12px;
    transform: translate(-50%,0);
    cursor: pointer;
}

@media screen and (max-width: 768px) {
    .app {
        max-width: 100%;
        margin: 0 ;
    }
    .background-container {
        position: relative;
        width: 100%;
        height: 100vh;
        margin-top: 0 ;
        overflow: hidden;
    }
    .background-container img {
        width: 100%;
        height: 100%;
    }
}